The demand for pine trees to make wood products continues to increase. One proposed solution to this problem is to identify individual trees that possess desirable characteristics, such as a rapid rate of growth, and produce numerous, genetically identical, clones of the superior trees by somatic cloning. These clones can be cultivated to yield stands, or whole forests, of pine trees that possess the desirable characteristic(s).
One method for cloning pine trees utilizes in vitro treatment of isolated, living, pine tissue under conditions that promote formation of pine embryos, and then whole plants, from the treated tissue. The isolated pine tissue may be cultured in the presence of one or more auxins, and/or cytokinins, to promote formation and multiplication of embryogenic tissue that is then cultured under conditions that promote formation of cotyledonary pine embryos. The embryos may then be germinated to yield pine trees. An example of pine embryogenic tissue are embryonal suspensor masses (ESMs) that can be formed, by tissue culture in vitro, from pine embryos dissected from pine seeds. FIG. 1 shows pine embryonal suspensor masses in liquid culture. FIG. 2 shows a cotyledonary pine embryo formed from ESM (cotyledons are visible at the top of the embryo).
A continuing problem, however, is stimulating efficient formation of cotyledonary pine embryos that are capable of germinating with high frequency to yield pine plants. Preferably the cotyledonary pine embryos, formed in vitro, are morphologically, anatomically and biochemically similar, or identical, to zygotic pine embryos formed, in vivo, in pine seeds. In particular, there is a need for methods for producing, in vitro, greater numbers of zygotic-like cotyledonary pine embryos than are produced by prior art methods. Preferably, the germination frequency and quality of the cotyledonary pine embryos produced by the novel methods should be higher than the germination frequency and quality of cotyledonary pine embryos produced by prior art methods.